This differs from traditional Spring singletons in that it exposes attributes in the
ServletContext. Those attributes will get destroyed whenever the entire application
shuts down, which might be earlier or later than the shutdown of the containing Spring
ApplicationContext.

getConversationId()
Return the conversation ID for the current underlying scope, if any.

void

registerDestructionCallback(String name,
Runnable callback)
Register a callback to be executed on destruction of the specified
object in the scope (or at destruction of the entire scope, if the
scope does not destroy individual objects but rather only terminates
in its entirety).

remove

Returns null if no object was found; otherwise
returns the removed Object.

Note that an implementation should also remove a registered destruction
callback for the specified object, if any. It does, however, not
need to execute a registered destruction callback in this case,
since the object will be destroyed by the caller (if appropriate).

Note: This is an optional operation. Implementations may throw
UnsupportedOperationException if they do not support explicitly
removing an object.

registerDestructionCallback

Register a callback to be executed on destruction of the specified
object in the scope (or at destruction of the entire scope, if the
scope does not destroy individual objects but rather only terminates
in its entirety).

Note: This is an optional operation. This method will only
be called for scoped beans with actual destruction configuration
(DisposableBean, destroy-method, DestructionAwareBeanPostProcessor).
Implementations should do their best to execute a given callback
at the appropriate time. If such a callback is not supported by the
underlying runtime environment at all, the callback must be
ignored and a corresponding warning should be logged.

Note that 'destruction' refers to to automatic destruction of
the object as part of the scope's own lifecycle, not to the individual
scoped object having been explicitly removed by the application.
If a scoped object gets removed via this facade's Scope.remove(String)
method, any registered destruction callback should be removed as well,
assuming that the removed object will be reused or manually destroyed.

callback - the destruction callback to be executed.
Note that the passed-in Runnable will never throw an exception,
so it can safely be executed without an enclosing try-catch block.
Furthermore, the Runnable will usually be serializable, provided
that its target object is serializable as well.

getConversationId

The exact meaning of the conversation ID depends on the underlying
storage mechanism. In the case of session-scoped objects, the
conversation ID would typically be equal to (or derived from) the
session ID; in the
case of a custom conversation that sits within the overall session,
the specific ID for the current conversation would be appropriate.

Note: This is an optional operation. It is perfectly valid to
return null in an implementation of this method if the
underlying storage mechanism has no obvious candidate for such an ID.